Gas discharge display device with perimetrical cathode

ABSTRACT

A display device employing a planar array of elements disposed on a dielectric substrate. The dielectric substrate is affixed to a metallic plate which functions as an anode element in an electrical discharge while a perimetrical metallic strip serves as a cathode element. These components are disposed between two non-conductive plates in which a partial vacuum is created and backfilled with an inert gas. The non-conductive plate proximate the display surface of the array of elements is transparent enabling an undistorted view of the segments. A relatively large potential applied between the anode and the cathode elements sustains the electrical discharge thereby providing a source of free electrons in the area between the elements and the transparent plate. The application of a small bias voltage between selected segments of the array of elements and the anode element produces a thin luminous sheath over the energized segments which provides a sharply defined display.

United States Patent Veron GAS DISCHARGE DISPLAY DEVICE WITHPERIMETRICAL CATI'IODE Inventor: Harry Veron, Framingham, Mass.

Assignee: Sperry Rand Corporation Filed: July l0,- 1970 Appl. No.:52,761

U.S.Cl. ..3l5/l69 TV,3l3/l09.5,313/2l0, 313/217, 313/220 Int. Cl. ..H05b37/00 Field of Search ..313/109.5, 210, 209, 217, 220; 315/169 R, 169 TVReferences Cited UNITED STATES PATENTS Kayatt Primary Erandner-Roy LakeAssistant Examiner-Palmer C. Demeo Attorney-S. C. Yeaton ABSTRACT Adisplay device employing a planar array of elements disposed on adielectric substrate. The dielectric substrate is affixed to a metallicplate which functions as an anode element in an electrical dischargewhile a perimetrical metallic strip serves as a cathode element. Thesecomponents are disposed between two non-conductive plates in which apartial vacuum is created and backfilled with an inert gas. Thenonconductive plate proximate the display surface of the array ofelements is transparent enabling an undistorted view of the segments. Arelatively large potential applied between the anode and the cathodeelements sustains the electrical discharge thereby providing a source offree electrons in the area between the elements and the transparentplate. The application of a small bias voltage between selected segmentsof the array of elements and the anode element produces a thin luminoussheath over the energized segments which provides a sharply defineddisplay.

6 Claims, 1 Drawing Figure PATENTEBJum 1972 3.670.201

V IN new we HA RR) VERON ATTORNEY:

1 GAS DISCHARGE DISPLAY DEVICE WITH PERIME'I'RICAL CATI-IODE BACKGROUNDOF THE INVENTION 1. Field of the Invention The disclosed inventionpertains to the field of displays and .more specifically to displaysutilizing an electrical dischargein a gas.

2. Description of the Prior Art Gas discharge display devices usuallyemploy a luminous portion of an electrical discharge through a gas aspart of the illumination for the display elements. This discharge isreferred to as a glow discharge and is produced between an anode elementand a cathode element by inelastic collisions of electrons and atoms ofthe gas. These collisions'cause electrons in high energy levels of theatoms to rise to higher levels, then eventually fall back and releasephotons. To provide a sustained glow discharge, a relatively largeelectric field is applied between the anode and cathode to impart highacceleration to the free electrons initially present between theelements. The highly accelerated electrons collide with atoms of the gasfreeing electrons in the higher energy levels of the atoms. Theremaining gas atoms are then ionized and accelerated toward the cathodeelement. When the ionized atoms impinge on the surface of the cathodethey produce more free electrons which are then accelerated toward theanode resulting in a sufficient number of collisions with atoms of thegas to maintain the glow discharge.

The most frequently employed portion of a cold-cathode discharge is thenegative glow which occurs near the cathode. This negative glow usuallyemits diffuse illumination and therefore requires some externalfiltering or other means to sharpen the resulting image of the cathodedisplay elements. The dimming capability of such a display is limited inthat there is a relatively high minimum voltage below which thedischarge will not be maintained, that is, the device isnot continuouslydimmable to zero light output.

Moreover, the lifetime of a gas discharge display device is limited bysputtering which is the rate that material is emitted or eroded from thecathode. Material is removed from the cathode element as a result of theionized gas atoms impinging on the surface of the cathode. The rate atwhich material is removed from the cathode is related to the number ofions and the energy of the ions impinging on the cathode. Removal of anappreciable amount of material from the cathode element causes changesin the electrical characteristics of the display and increases theprobability of short-circuiting the display elements. In the prior artdevices the large voltage drops in the cathode region imparted largeenergy levels to the ions thereby increasing the rate at which materialwas removed from the cathode and decreased the life of the display.

SUMMARY OF THE INVENTION The present invention provides a displayincluding a plurality of thin film metallic elements disposed on adielectric substrate which is epoxied to a metallic plate. The metallicplate is and centrally disposed with respect to a perimetrical metallicstrip. These components are afiixed to a portion of a dielectricmaterial which is used as a backing surface. Energized segments of thethin film metallic elements are viewed through a second transparentportion of dielectric material which is mounted over the components.

Initially a vacuum is created in the space bounded by the two dielectricplates and the perimetrical metal strip. Subsequently, an inert gas suchas neon is then partially backfilled into the vacuum. A relatively largepotential is applied between the metallic plate which functions as ananode and the perimetrical metallic strip which serves as a cathodethereby maintaining an electrical discharge. The electrical dischargeprovides a source of free electrons over the area of the anode. Lowlevel bias voltages are applied between the anode and selected segmentsof the thin film metallic elements which accelerate the electrons in thearea immediately in front of the energized segments. A thin luminoussheath is produced in front of each energized segment that isessentially a type of anodeglow from which a sharply defined image isobtained. The thin luminous sheath over the energized segments is aspatial charge region due mainly to electrons.

The number of electrons and the associated energy of these electrons arerelatively small because the bias voltage levels are low. Consequently,the rate at which material is removed from the energized elements is lowand the life of the display is increased.

Since the bias voltage levels which are used to energize selectedsegments of the display elements are low, the device can be readilyadapted for use with digital logic circuitry with a minimum ofinterfacing electronics. Further, the luminosity of the display can bevaried without changing the voltage level between the anode and cathodethat sustains the electrical discharge, thereby enabling the luminosityto be continuously dimmed to zero light output.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE is an isometric viewincluding a partial schematic diagram of an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT I form the inverse brush cathode11. A metallic anode plate 13 is centrally disposed within the ring .11and also may be fabricated from aluminum. Affixed to the plate 13 is apiece of dielectric material 14 that may be comprised of a glasssubstrate. A plurality of display elements 15 are disposed on thedielectric material 14 and are coplanar with the anode plate 13. Y

The plurality of display elements 15 can be thin metallic filmsincluding, for example, stainless steel. These components are interposedbetween two circular plates 16 and 17 to form an integral tube unit. Thecircular plate 16, which covers the front of the displaydevice 10, istransparent to allow. direct viewing of the display elements 15. Theback plate 17 has a centrally located opening 23 in which the anodeplate 13 is secured with an adhesive sealant. vA vacuum is createdwithin the tube unit by attaching a vacuum pump to access port 18 andreducing the pressure. The .unit is then partially backfilled throughthe access port 18 with a typical inert gas such as neon. The inversebrush cathode 11 is connected to the negative terminal of a d.c. voltagesource 19. The anode plate 13, the positive terminal of the d.c.voltagev source 19 and the negative terminal of the d.c. bias voltagesource 20 are maintained at ground potential. The positive terminal ofthe d.c. bias source 20 is coupled to the plurality of display elements15 through variable resistance 21 and a plurality of switches 22. DCvoltage source 19 applies a relatively large potential between the anodeplate 13 and the inverse brush cathode 11 to provide a source of freeelectrons in an inverse brush electrical discharge.

It is known that the grazing incidence of ions on a metallic surfacegreatly increases the secondary electron yield per ion over directincidence of ions on a metal surface. In the inverse brush cathode, thesurface areas of the holes 12 are nearly parallel to the incoming ions.Therefore, a larger number of ions will graze the surface areas in theinverse brush cathode than in a flat cathode. As a result, the inversebrush cathode produces a larger number of electrons per unit area than aflat cathode operating under the same conditions. The resulting inversebrush electrical discharge produces a dim glow over the area enclosed bythe inverse brush cathode. Activating specific switches of the pluralityof switches 22 applies a relatively low level bias potential from thed.c. bias source 20 to selected segments of the plurality of displayelements 15. This potential energizes the selected segments andaccelerates the electrons immediately in front of the energized segmentsthereby causing an increase in collisions between these electrons andatoms of the gas. As a result, a luminosity is observed above eachenergized segment which is essentially a type of anode glow. This typeof glow is very sharply defined and covers a small region just forwardof each energized segment. The intensity of the glow produced is muchgreater than the dim glow due to the inverse brush electrical dischargeand sufficient contrast is provided to be visible in room light. In oneembodiment of the invention, the contrast was increased by masking of?the area around the anode plate 13.

In a specific embodiment of the present invention the inverse brushcathode I1 and the anode plate 13 were fabricated from aluminum. Thedisplay elements 15 were deposits of stainless steel films approximately1,500 Angstroms thick on a glass substrate which measured 1.0 by 0.6inches. A fixed format numeric display was used with each number 8element measuring typically %-inch high by rii-inch wide. The inversebrush cathode 11 was secured to a back plate 17 which comprised acircular piece of Pyrex having an opening 23, centrally positioned withrespect to the inverse brush cathode 11. The anode plate 13 was affixedwithin the opening 23 with an adhesive. A second circular piece of Pyrexwas attached to the front of the inverse brush cathode l1 and permitteddirect viewing of the display elements 15. The assembled unit was placedon a vacuum station and pumped down to a pressure of approximately 10'torr and then backfilled with neon to a pressure of about 0.3 torr. Aninverse brush electrical discharge was maintained by applying apotential of 500 volts d.c. between the cathode 11 and the anode 13. Thecurrent through the discharge was maintained at 2.5 milliamps using a40K ohm ballast resistor in series with the dc. voltage source 19 andthe cathode 11. Typical bias voltages between the display elements 15and ground ranged from 3 to +10 volts do. and the corresponding currentsranged from 0.25 to 1.7 milliamps. The biasing voltage range to go fromzero to visible light output in room light was a function of the numberof segments energized, the gas pressure in the tube and the voltagebetween the cathode l1 and the anode 13.

Because the power consumption for this type display is in the milliwattrange and the voltage levels are low, the display is extremelyattractive in that the entire display can be energized directly fromdigital logic circuitry with minimal interfacing electronics. Further,the bias voltage with respect to the anode is low and electronsaccelerated through small voltage drops are not likely sputteringagents; therefore, the life of the display is extended.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes may be made withinthe purview of the appended claims without departing from the true scopeand spirit of the invention in its broader aspects.

lclaim:

1. A display device comprising,

vacuum tube means having a transparent viewing surface and partiallyfilled with an inert gas,

perimetrical cathode means disposed behind said viewing surface,

anode plate means centrally disposed with respect to said perimetricalcathode means,

a source of voltage coupled between said cathode means and said anodemeans for providing a source of free electrons in an electricaldischarge within the space bounded by said perimetrical cathode means,

dielectric means disposed within said anode plate means,

display element means having a plurality of segments affixed to saiddielectric means and substantially co-planar with said anode means,

bias voltage means, and

switching means connected between said bias voltage means and saiddisplay element means for energizing selected segments of said pluralityof segments which accelerates free electrons in said electricaldischarge which are proximate said energized selected segments therebyproducing a sharply defined luminous image over said selected segments.

2. A display device as described in claim 1 in which said displayelement means include thin metallic strips in a fixed format numericdisplay.

3. A display device as described in claim 1 in which said perimetricalcathode means includes means for providing an inverse brush discharge.

4. A display device as described in claim 1 in which said bias voltagemeans is a low level voltage including a variable voltage means forproviding continuous dimming to zero light output of said sharplydefined luminous image.

5. A display device as described in claim I in which said switchingmeans includes integrated switching circuits.

6. A display device comprising a backing plate, a transparent coverplate and an aluminum perimetrical strip disposed between said backingplate and said cover plate enclosing a vacuum that is partiallybackfilled with an inert gas such as neon, said aluminum strip havingholes drilled into its interior surface to enable said strip to functionas an inverse brush cathode, an aluminum plate affixed to said backingplate and centrally disposed with respect to said aluminum strip, aglass substrate mounted within said aluminum plate, display elementsdisposed on said glass substrate, supply voltage means connected betweensaid aluminum strip, functioning as an inverse brush cathode, and saidaluminum plate, serving as an anode connected to ground, said supplyvoltage means producing a source of free electrons in an inverse brushelectrical discharge, variable low level bias voltage means appliedbetween said display elements and said anode, and integrated circuitswitching means for connecting said variable bias voltage means toselected segments of said display elements producing a sharply definedluminous image of said selected segments.

1. A display device comprising, vacuum tube means having a transparentviewing surface and partially filled with an inert gas, perimetricalcathode means disposed behind said viewing surface, anode plate meanscentrally disposed with respect to said perimetrical cathode means, asource of voltage coupled between said cathode means and said anodemeans for providing a source of free electrons in an electricaldischarge within the space bounded by said perimetrical cathode means,dielectric means disposed within said anode plate means, display elementmeans having a plurality of segments affixed to said dielectric meansand substantially co-planar with said anode means, bias voltage means,and switching means connected between said bias voltage means and saiddisplay element means for energizing selected segments of said pluralityof segments which accelerates free electrons in said electricaldischarge which are proximate said energized selected segments therebyproducing a sharply defined luminous image over said selected segments.2. A display device as described in claim 1 in which said displayelement means include thin metallic strips in a fixed format numericdisplay.
 3. A display device as described in claim 1 in which saidperimetrical cathode means includes means for providing an inverse brushdischarge.
 4. A display device as described in claim 1 in which saidbias voltage means is a low level voltage including a variable voltagemeans for providing continuous dimming to zero light output of saidsharply defined luminous image.
 5. A display device as described inclaim 1 in which said switching means includes integrated switchingcircuits.
 6. A display device comprising a backing plate, a transparentcover plate and an aluminum perimetrical strip disposed between saidbacking plate and said cover plate enclosing a vacuum that is partiallybackfilled with an inert gas such as neon, said aluminum strip havingholes drilled into its interior surface to enable said strip to functionas an inverse brush cathode, an aluminum plate affixed to said backingplate and centrally disposed with respect to said aluminum strip, aglass substrate mounted within said aluminum plate, display elementsdisposed on said glass substrate, supply voltage means connected betweensaid aluminum strip, functioning as an inverse brush cathode, and saidaluminum plate, serving as an anode connected to ground, said supplyvoltage means producing a source of free electrons in an inverse brushelectrical discharge, variable low level bias voltage means appliedbetween said display elements and said anode, and integrated circuitswitching means for connecting said variable bias voltage means toselected segments of said display elements producing a sharply definedluminous image of said selected segments.